The present invention relates generally to audio line isolators. More particularly, the present invention relates to multiple suite audio line isolators.
Section 3.2.4.19.10 of the Canadian National Building Code states that damage to or disconnection of an audible signal device in a dwelling unit may not interfere with the ability of devices outside the dwelling unit to sound an alarm.
Existing line isolation devices designed to serve this function in systems using 70 v audio signaling have significant reaction times, require the presence of audio on power-up to perform fault isolation, and require the presence of an audio signal to maintain isolation. These limitations make the existing designs unacceptable for use with amplifiers which have fault sensing capabilities.
Existing designs presently use Polymeric Positive Temperature Coefficient devices, otherwise known as PPTCs, to provide passive isolation of short circuit conditions on audio lines. These devices are thermal in nature, requiring the initial presence of high values of current on the audio line before any isolation can take place. The lower current values associated with 70 v audio and the significantly long reaction times inherent in the nature of PPTCs make them unsuitable for use in this application.
The thermal nature of PPTCs also results in significant sensitivity to ambient temperature conditions. Trip and hold currents for PPTCs typically used in this application are derated as much as 25% over the 0 to 49xc2x0 C. rated temperature range.
The present invention operates to perform isolation independent of temperature effects over its rated range.
The device uses a low value resistance in parallel with the detector of an optoisolator to sense peak current values and subsequent loading being presented by the audio signaling devices in a dwelling unit. When the peak current value exceeds a point dictated by the value of the resistor, the output side of the optoisolator becomes active. This activity is sampled and initiates activation of a relay used to isolate the dwelling unit from the audio circuit. Activation of the coil of the relay for approximately 500 uS initiates electronic latching of the isolation relay. Subsequent isolation is independent of the presence of audio, resulting in a device which has a very fast reaction time, and has no reliance on the continued presence of an audio signal to maintain isolation.
An audio amplifier which has fault sensing capabilities will typically not attempt to supply audio into a short circuit condition. A timing circuit is incorporated into this design to activate the isolation relays for the first 2.7 seconds on presentation of the alarm. Momentary clearance of any short that may have been present gives an amplifier with short sensing capabilities a window of opportunity to supply audio. This audio will subsequently be used by the isolator to perform sensing when the timer circuit releases control of the isolation relay.
Supervision switching is designed to be compatible with class A or class B supervision, and allows the use of a single sensing and isolating element to monitor for short circuit conditions in the dwelling unit.
In one embodiment of the invention, a method for isolating suites includes the steps of isolating the suites when an alarm is initiated, setting a timer during isolation creating a window of time to clear a short circuit, clearing the short circuit, removing isolation from the suites as the timer reaches completion, determining if there is a short circuit in each of the suites, and isolating suites that have a short circuit.
In another embodiment of the invention, a line isolator for multiple suites includes a supervisory relay capable of supplying power to suites in series and in parallel, and an isolation relay in communication with the supervisory relay. The isolation relay prevents power from being supplied to a suite. Sense circuitry is in communication with the isolation relay. The sense circuitry determines if there is a short circuit. Latching circuitry is in communication with the sense circuitry. The latching circuitry activates the isolation relay to prevent power from being supplied to a suite when the sense circuitry determines the occurrence of a short circuit. A timer is in communication with the latching circuitry. The timer allows time for a short circuit to be cleared during isolation.
In an alternate embodiment, a line isolator system for multiple suites includes a supervisory relay means for supplying power to suites in series and in parallel and an isolation relay means for preventing power from being supplied to a suite. The isolation relay means is in communication with the supervisory relay means. A sense circuitry means is provided for determining if there is a short circuit and is in communication the isolation relay means. A latching circuitry means is provided for activating the isolation relay means to prevent power from being supplied to a suite when the sense circuitry means determines the occurrence of a short circuit. The latching circuitry means is in communication with the sense circuitry means. A timer means is provided for creating a time period during isolation to allow a short circuit to be cleared. The timer means is in communication with the latching circuitry means.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract included below, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.